I agree that if the outlet that serves the fridge is within 6 feet of the sink, it requires GFCI protection. But it would be a poor kitchen design that had the fridge and the sink immediately adjacent to each other. A good kitchen layout would have counter space on both sides of the sink, so that the outlet that serves the fridge would likely be more than 6 feet away.
I don't think the rule applies to outlets within cabinets or around corners. As to the meaning of "within 6 feet," my interpretation is that if you hold one end of a 6' long string at the edge of the sink, any outlet that can be reached by the other end needs GFCI protection. So in the case of the fridge, with a 2 foot counter space next to the sink, and with the outlet that serves the fridge located close to floor level, the 6' long string would not reach the outlet. I reiterate that if in order to get to the outlet with the string you first have to open a cabinet door, the rule does not apply.
I know that this isn't in the code, but by my way of thinking the reason for the 6' rule is that portable appliances (e.g., blenders and toasters) have power cords of that length or shorter. So the rule is all about the risk of dropping the appliance into a sink full of water with the appliance still being plugged into the outlet. We don't typically open the cabinet door above the stove (where the microwave is located) or below the sink (where the disposal is located), and use the outlet to plug in a portable appliance.